----------------------------
"daestrom" wrote in message
...

wrote in message
...
In alt.engineering.electrical Michael Moroney
wrote:

| Are the load tap generators configured make-before-break?
| Break-before-make would mean a (very short) power outage every
activation
| but make-before-break would mean a momentarily short-circuited winding
and
| the break would involve interrupting a large short circuit current.

I wonder how much regulation could be managed through the use of variable
leakage inductance in the transformer windings.


I suppose you could, but increasing leakage inductance means you're
increasing losses aren't you? Just a percent or two on a unit rated for
250 MVA can be too much to tolerate.

daestrom
-------------
I don't see changing leakage inductance having much effect on losses ( a
great effect on voltage regulation -likely all to the bad) but the problem
is one of changing leakage inductance.
Does this mean changing a gap in the core? Does it mean moving one winding
with respect to another? In any case it does mean some fiddling with the
core or winding.
This has been done for series lighting circuits where the load current was
kept constant by using a transformer which balanced the forces between coils
against a fixed weight. If the current changed the secondary coil moved so
that there was more or less leakage. The units that I have seen were rather
cumbersome.

--

Don Kelly
remove the X to answer

"Michael A. Terrell" writes:

wrote:

In sci.electronics.repair jakdedert wrote:
I'm a little confused about a 230 volt circuit. In what part of the
world does the utility supply 230v?

Continental Europe used to have 220 volts (before that it was 127 volts in
some places), the UK used to have 240 volts. Nowadays, the common voltage
is 230 volts -10% +6%.


In other words, nothing has changed. They just wrote sloppier specs.

It has changed, the voltage is now close to 230V, at least in Sweden.

I guess the sloppiness was specified to allow a gradual switch from
220/240 to 230 and still be within spec.

Residential power in Norway is normally 230V three phase btw, instead
of 400V three phase. Their 230V outlets are two phase and ground
instead of one phase, neutral and ground. Their three phase outlets
therefore are blue instead of red and have four prongs instead of five.

Thomas Tornblom wrote:

"Michael A. Terrell" writes:

wrote:

In sci.electronics.repair jakdedert wrote:
I'm a little confused about a 230 volt circuit. In what part of the
world does the utility supply 230v?

Continental Europe used to have 220 volts (before that it was 127 volts in
some places), the UK used to have 240 volts. Nowadays, the common voltage
is 230 volts -10% +6%.


In other words, nothing has changed. They just wrote sloppier specs.

It has changed, the voltage is now close to 230V, at least in Sweden.

I guess the sloppiness was specified to allow a gradual switch from
220/240 to 230 and still be within spec.

Residential power in Norway is normally 230V three phase btw, instead
of 400V three phase. Their 230V outlets are two phase and ground
instead of one phase, neutral and ground. Their three phase outlets
therefore are blue instead of red and have four prongs instead of five.


Do the math. The specifications allow continued use of the old
standard n each country.

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"Michael A. Terrell" writes:

Thomas Tornblom wrote:

"Michael A. Terrell" writes:

wrote:

In sci.electronics.repair jakdedert wrote:
I'm a little confused about a 230 volt circuit. In what part of the
world does the utility supply 230v?

Continental Europe used to have 220 volts (before that it was 127 volts in
some places), the UK used to have 240 volts. Nowadays, the common voltage
is 230 volts -10% +6%.


In other words, nothing has changed. They just wrote sloppier specs.

It has changed, the voltage is now close to 230V, at least in Sweden.

I guess the sloppiness was specified to allow a gradual switch from
220/240 to 230 and still be within spec.

Do the math. The specifications allow continued use of the old
standard n each country.

If you read my comment you will see that I agree that the new spec
covers the old voltages. I do not agree with your statement that
"nothing has changed". We had 220V before and we now have 230V, so the
actual voltage has definitely changed.

In message , Thomas Tornblom
writes
"Michael A. Terrell" writes:

Thomas Tornblom wrote:

"Michael A. Terrell" writes:

wrote:

In sci.electronics.repair jakdedert wrote:
I'm a little confused about a 230 volt circuit. In what part of the
world does the utility supply 230v?

Continental Europe used to have 220 volts (before that it was 127
volts in
some places), the UK used to have 240 volts. Nowadays, the common voltage
is 230 volts -10% +6%.


In other words, nothing has changed. They just wrote sloppier specs.

It has changed, the voltage is now close to 230V, at least in Sweden.

I guess the sloppiness was specified to allow a gradual switch from
220/240 to 230 and still be within spec.

Do the math. The specifications allow continued use of the old
standard n each country.

If you read my comment you will see that I agree that the new spec
covers the old voltages. I do not agree with your statement that
"nothing has changed". We had 220V before and we now have 230V, so the
actual voltage has definitely changed.

In the UK, we had 240V. We now have err..... 240V.
There may be places where it really has been reduced to 230V, but I've
never been anywhere where I had occasion to measure the mains voltage,
and didn't get around 240V - certainly not sufficiently different for
you to notice the difference.
--
Ian

? "daestrom" ?????? ??? ??????
...

"Michael Moroney" wrote in message
...
"daestrom" writes:


P.S. In the US, a 'tap-changer' may be built for either for unloaded or
loaded operation. The 'unloaded' type can not be stepped to another tap
while there is load on the unit (although it can still be energized).
It's
switch contacts cannot interrupt load though, so if you try to move it
while
loaded, you can burn up the tap-changer. The classic 'load-tap-changer'
is
actually several switches that are controlled in a precise sequence to
shift
the load from one tap of the transformer to another while not
interrupting
the load current.

P.P.S. Load tap changers typically have a significant time-delay built
into
the controls so they do not 'hunt' or respond to short drops in voltage
such
as starting a large load. 15 seconds to several minutes is typical. So
even with load-tap-changers, starting a single load that is a high
percentage of the system capacity will *still* result in a voltage dip.

Are the load tap generators configured make-before-break?
Break-before-make would mean a (very short) power outage every activation
but make-before-break would mean a momentarily short-circuited winding
and
the break would involve interrupting a large short circuit current.

Certainly modern ones likely use thyristors and zero crossing detectors.


I figured someone would 'bite' :-)

Typical large power load-tap-changers have a primary winding and two
secondaries.
You mean a secondary and a tetriary? The transformer for the hotel load of a
300 MW unit is powered directly from the turbo alternator (21 kV) and has a
secondary of 6.6 kV and a tetriary of again 6.6 kV. This is done because it
has wye-wye-wye connection (IIRC). The hotel load of such a unit is 10%,
also 30 MW, including 7 brown coal mills. Typical size of a 6.6 kV motor is
1 MW.
One secondary produces about 100% of 'rated' secondary voltage. The second
secondary produces about 15% to 20% of the rated voltage, but has numerous
taps from end to end, about 2.5% 'steps'. (for a total of about eight
taps). The cental tap of the boost/buck winding is tied to one end of the
main secondary. The boost/buck can be used to step from 90% to 110% of the
'design' output. I suppose some can step over a wider range, but I haven't
run across them.

*TWO* rotary switches have each tap tied to one of the positions of each
rotory switch, and each 'wiper' is tied to single heavier contacts that
are opened in the operating sequence. The output side of these two
interrupting contacts are tied to each end of a large center-tapped
inductor.

So, normally both rotary switches are aligned to the same transformer tap,
both interrupting contacts are shut, and load current flows from the
boost/buck winding tap, splits and flows through both rotary switches,
both interrupting contacts, enters both ends of the inductor and out the
inductor center tap. Because the current flows into both ends of the
inductor and the mutual inductance of the two parts cancel, there is
little voltage drop in the inductor.

Begin step sequence:
1) Open one interrupting contactor. Now load current doubles through half
the inductor and is zero in the other half, so the voltage drop across the
inductor actually makes output voltage drop, even if trying to step 'up'.
2) Move associated rotary switch to next step of transformer bank.
3) Close interrupting contactor. Now, the two rotary switches are across
different taps. The inductor prevents a excessive current, otherwise you
have a direct short of the two winding taps. Some tap changers can stop
at this point and are called 'half-step' units. Obviously, the inductor
has to be rated for sustained operation across a step of the boost/buck
winding plus load current in order to survive sustained 'half step'
operation.
4) But for tap changers that can't operate 'half-step', the sequence
continues. And opens the other interrupting contactor. Now the other
half of the inductor has full load current.
5) Move second rotary switch to next step (now both switches are on the
new step)
6) Close the second interrupting contactor. You're back in the initial
configuration, but with both rotary switches on a new transformer tap.
Quite the same principle is done with diesel locomotives and is called
diesel-electric transmission, and also in pure electric locomotives (E-Lok
in german, for Elektrische Lokomotive). The diesel engine, 2-stroke and
usually 600 to 900 rpm at full throttle, is coupled to a generator. The
generator has small windings, connected in series for the last notch, higher
voltage and relatively smaller current, and in parallel for start, higher
amperage and smaller voltage. The traction motors are directly coupled on
the wheel shaft, and are air cooled. An E-Lok has a trasformer, with the
primary directly supplied by the cetenary, 15 kV 16 2/3 Hz in Germany, and
25 kV 50 Hz in Greece, The secondary uses the same principle. The typical
size of a traction motor is 1 MW, 4 (one each shaft) and maximum voltage 700
volts, and are series wound motors with special construction to operate at
16 2/3 Hz (or 50 Hz with today's technology). Typical power of a diesel
locomotive is 2850 HP, while an electric is 6000 HP. with 1500 HP at each
shaft, also ~1MW. There is a heavy duty 12,000 HP diesel engine in USA(with
6 shafts, also 2000 HP at each shaft). The high speed ICE train
(InterCityExpress) in germany is 13,000 HP, has a normal travelling speed of
200 km/h, 2 locomotives, 3-phase induction motors, electronic drive.
Older units do this whole thing with a fancy cam/gear arrangement circa
1940's. Just takes a single reversable motor to drive the unit and some
limit switches to be sure it can only stop at full 'steps' (or 'half
steps' for those capable of running 'half-step')

The one we have here operates with a motor.
Because the system intermittently inserts an additional voltage drop
through the inductor, the control circuits typically have time-delays that
prevent it trying to reverse direction or something while stepping.

As far as zero-crossing and thyristors, I suppose it's certainly possible,
but I haven't run across them for large substations. I have seen such a
setup in power-conditioners for computer complexes and such, but that's
only a few kVA (one unit I know of was rated for 25 kVA).

The mechanical-switch tap changer is well-matured and has the nice
advantage that when they 'fail', they 'fail' at the last 'step' and power
continues to flow (albeit perhaps the wrong voltage).

When I was a kid living in a rather rural area, there would be a pair of
these on poles every few miles, connected open delta. (all transformer
primaries were connected phase-phase then).

Those are smaller than the units I'm thinking of. I'm talking about
multiple MVA rated units.

I had no idea how it really works, but I got the general idea.

--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

Ï Ýãñáøå óôï ìÞíõìá
...
In alt.engineering.electrical Tzortzakakis Dimitrios
wrote:

| A shame that Tesla won the infamous "battle" and we don't have DC:-()
But
| then, we would be having a power plant at each neighborhood, instead of
the
| 300 MW ones.

And the latter make easy terrorism targets, too.

I cross my fingers that terrorists get no electrical engineering degree:0

| I know, I know, my answer was a bit provocative:-) And of course there
are
| DC regulators.... You're talking about DC generators;the one a 300 MW
uses
| for excitation is 220 V, 1000 A DC and probably shunt field. I have seen
| here in some machine shops the old type welding generator, which is a 3
| phase induction motor coupled to (usually) a compound field DC
generator,
| which provides the welding current. The modern ones are, maybe, not
larger
| than a shoe box and powered by a higher wattage 230 V 16 A receptacle.
| (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and
the
| like).

You don't use 400 V for anything heavy duty like an oven?

Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and
earth, goes without saying). Just if you connect it on 1 phase (as usually)
you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230 V is
powerful enough for almost everything in a house, only large airconditioners
are 3 phase, and all industrial motors, even if they are 1HP:-) (




--

--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

"Don Kelly" writes:

"Michael Moroney" wrote in message
...

Are the load tap generators configured make-before-break?
Break-before-make would mean a (very short) power outage every activation
but make-before-break would mean a momentarily short-circuited winding and
the break would involve interrupting a large short circuit current.
--------
Yes -you are shorting a part of the winding but the switching is a bit more
complex than that so that short circuit currents are limited to reasonable
values. It is a multistep operation with reactor switching. ...

Thanks for your (and esp. daestrom's) explanation on how they work.

When I was a kid living in a rather rural area, there would be a pair of
these on poles every few miles, connected open delta. (all transformer
primaries were connected phase-phase then).

"on load tap changers"? Not likely. These were applied to transformers only
where it was worth the effort.
Definitely transformers in rural areas- typical pole pigs- would have to be
de-energized as the tap changer is a manually operated switch inside the
tank. Some larger transformers did have off-load but live changers operated
from ground level. What you saw could have been somethng else altogether.

I'm not completely sure what these are other than being told that they
were voltage regulators (tapped autotransformers) long ago. These are
large cans with 3 bushings on top, taller and slimmer than most pole pigs,
and they usually have a control box on the pole around eye level. I see
the same style cans in substations between the stepdown transformer and
the distribution system except they sit on the ground and come in sets of
three.

Delta primaries as you indicate were around when you were a kid, would, in
most areas mean that you are now a pensioner. I remember cases of conversion
from delta to star for distribution primaries in small towns being done
about 60 years ago and use of delta for transmission died much before that.

While I'm hardly a kid, I'm no pensioner yet. In fact my father's place
still has delta-connected distribution primaries in the area, at 7200
volts (I have an old fuse/switch holder from there labelled 7200V ??A).

Where I mentioned they had pairs of these "voltage regulators" (or
whatever they were) every several miles was a long run along a state
highway. At some point they upgraded it to a wye configuration, probably
at a higher voltage. However, several side branches haven't been upgraded
yet. On the side branch feeding my father's place there is a bank of 3
transformers connected wye-delta immediately followed by a pair of these
"voltage regulator" cans connected open delta. From that point on the
distribution system is visibly old.

Yep. Seen those types of units and was about to mention them. One
model had a core that had a space in it much like a D'Arsonval meter
movement. The space was filled with a 'bobbin' that when cross-ways left
two large air-gaps and when aligned would neatly bring the gap between
the two sides of the core. A weight and lever would turn the 'bobbin'
into/outof the core to control the current.

Problem with those is, if you get a loose connection or arc, the unit
will just keep pumping power to the system no matter what.

daestrom



The only place I've seen those used was for regulating current in 6.6A
(usually) series loop streetlighting. Lots of this still left in the Los
Angeles area and a few other pockets but most is gone by now. It was
very common from the 20s up through the 60s though, incandescent at
first, but 6.6A matching transformer "ballasts" are available for HID
lamps as well. Most airfield illumination is still 6.6A series, I
suspect the modern control gear is solid state.

Westinghouse had a design where the secondary was on a linear mechanism
with a counterweight and would float above the primary. Current was
adjusted by moving the counterweight.

In alt.engineering.electrical Tzortzakakis Dimitrios wrote:
|
| ? ?????? ??? ??????
| ...
| In alt.engineering.electrical Tzortzakakis Dimitrios
| wrote:
|
| | A shame that Tesla won the infamous "battle" and we don't have DC:-()
| But
| | then, we would be having a power plant at each neighborhood, instead of
| the
| | 300 MW ones.
|
| And the latter make easy terrorism targets, too.
|
| I cross my fingers that terrorists get no electrical engineering degree:0

I suspect quite many already have them. Many have degrees in a lot of other
things like chemistry and physics. Some even have doctoral level degrees.


| | I know, I know, my answer was a bit provocative:-) And of course there
| are
| | DC regulators.... You're talking about DC generators;the one a 300 MW
| uses
| | for excitation is 220 V, 1000 A DC and probably shunt field. I have seen
| | here in some machine shops the old type welding generator, which is a 3
| | phase induction motor coupled to (usually) a compound field DC
| generator,
| | which provides the welding current. The modern ones are, maybe, not
| larger
| | than a shoe box and powered by a higher wattage 230 V 16 A receptacle.
| | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and
| the
| | like).
|
| You don't use 400 V for anything heavy duty like an oven?
|
| Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and
| earth, goes without saying). Just if you connect it on 1 phase (as usually)
| you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230 V is
| powerful enough for almost everything in a house, only large airconditioners
| are 3 phase, and all industrial motors, even if they are 1HP:-) (

That means each element individually runs on 230 V and they just divided them
up in three approximately equal sections, or use triple elements for each type
of use.

How many things that have just ONE (large) element would have it available in
both 230 V and 400 V versions?

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Don Kelly wrote:
| ----------------------------
| "daestrom" wrote in message
| ...
|
| wrote in message
| ...
| In alt.engineering.electrical Michael Moroney
| wrote:
|
| | Are the load tap generators configured make-before-break?
| | Break-before-make would mean a (very short) power outage every
| activation
| | but make-before-break would mean a momentarily short-circuited winding
| and
| | the break would involve interrupting a large short circuit current.
|
| I wonder how much regulation could be managed through the use of variable
| leakage inductance in the transformer windings.
|
|
| I suppose you could, but increasing leakage inductance means you're
| increasing losses aren't you? Just a percent or two on a unit rated for
| 250 MVA can be too much to tolerate.
|
| daestrom
| -------------
| I don't see changing leakage inductance having much effect on losses ( a
| great effect on voltage regulation -likely all to the bad) but the problem
| is one of changing leakage inductance.
| Does this mean changing a gap in the core? Does it mean moving one winding
| with respect to another? In any case it does mean some fiddling with the
| core or winding.

The thought is to change the core in some way. Maybe that can be done in a
gradual way, as opposed to winding taps that have to be either BtM or MtB.


| This has been done for series lighting circuits where the load current was
| kept constant by using a transformer which balanced the forces between coils
| against a fixed weight. If the current changed the secondary coil moved so
| that there was more or less leakage. The units that I have seen were rather
| cumbersome.

I'm thinking more along the lines of a motor drive to move the coil, and
that be controlled by the same authority that would have controlled the
steppable taps.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Don Kelly wrote:

| Yes -you are shorting a part of the winding but the switching is a bit more
| complex than that so that short circuit currents are limited to reasonable
| values. It is a multistep operation with reactor switching. On-load tap
| changers are expensive and are generally limited to applications where this
| is absolutely needed (I have seen one where the tap changer was nearly as
| large as the transformer).

I was thinking of what I might do to get some fine voltage control within a
very limited range around 120 volts. The obvious option was a 0-140 volt
variable transformer. But I wanted to make sure I had a setup that could
be better limited, for example, to not allow an accidental too low voltage.
I also didn't want to run all the power through the variable. So what I
was going to do was get a smaller variable transformer, and two buck-boost
transformers. One transformer would be wired 120-16 in buck mode to drop
the voltage down to 104. The other transformer would be wired 120-24 and
supplied via the 0-140 variable transformer, giving me a 0-28 variable boost.
The end result is 104-132 over the full range of variable transformer control
(assuming the boost transformer has no issues with being overfed at 140V).

So I might envision a transformer where the taps can be part of a boost
transformer added to the main transformer. The first buck transformer in
my above example would not be needed because the main transformer would be
designed with a 1st secondary at the lowest voltage of the adjustable range.
A 2nd secondary on the same main transformer would have the adjustable taps
and it would feed a separate boost transformer which has a secondary wired
in series with the 1st secondary of the main. So the taps would only be
dealing directly with a fraction of the power (assuming there is no back
feed issue involved) based on the needed adjustment range.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Thomas Tornblom wrote:

| Residential power in Norway is normally 230V three phase btw, instead
| of 400V three phase. Their 230V outlets are two phase and ground
| instead of one phase, neutral and ground. Their three phase outlets
| therefore are blue instead of red and have four prongs instead of five.

Is this the system where the voltage is 133 volts relative to ground and 230
volts between phases (and formerly 127 volts relative to ground and 220 volts
between phases)?

If they still use that system, then I'm interested in buying a UPS designed
for that. But it is my understanding it is phased out in cities and hard to
find anymore in rural locations.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Ian Jackson wrote:
| In message , Thomas Tornblom
| writes
|"Michael A. Terrell" writes:
|
| Thomas Tornblom wrote:
|
| "Michael A. Terrell" writes:
|
| wrote:
|
| In sci.electronics.repair jakdedert wrote:
| I'm a little confused about a 230 volt circuit. In what part of the
| world does the utility supply 230v?
|
| Continental Europe used to have 220 volts (before that it was 127
| volts in
| some places), the UK used to have 240 volts. Nowadays, the common voltage
| is 230 volts -10% +6%.
|
|
| In other words, nothing has changed. They just wrote sloppier specs.
|
| It has changed, the voltage is now close to 230V, at least in Sweden.
|
| I guess the sloppiness was specified to allow a gradual switch from
| 220/240 to 230 and still be within spec.
|
| Do the math. The specifications allow continued use of the old
| standard n each country.
|
|If you read my comment you will see that I agree that the new spec
|covers the old voltages. I do not agree with your statement that
|"nothing has changed". We had 220V before and we now have 230V, so the
|actual voltage has definitely changed.
|
| In the UK, we had 240V. We now have err..... 240V.
| There may be places where it really has been reduced to 230V, but I've
| never been anywhere where I had occasion to measure the mains voltage,
| and didn't get around 240V - certainly not sufficiently different for
| you to notice the difference.

What I have heard is that teh distribution system is not changing, but new
service installations will be supplied with 230V unless 240V is specifically
requested ... after some point in time that may not have come, yet. What
I heard is they don't expect to have all of UK changed over for many decades,
and maybe even a century or so.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Don Kelly wrote:

| Yes -you are shorting a part of the winding but the switching is a bit more
| complex than that so that short circuit currents are limited to reasonable
| values. It is a multistep operation with reactor switching. On-load tap
| changers are expensive and are generally limited to applications where this
| is absolutely needed (I have seen one where the tap changer was nearly as
| large as the transformer).

What about multiple parallel transformers, or at least multiple parallel
windings on the same core (on whichever side the tapping is to be done),
where the taps are stepped incrementally on each winding? Instead of a
shorted winding segment, you'd have windings of differing voltage in
parallel as each of the windings change their taps one at a time.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

On 14 May 2008 01:35:23 GMT, wrote:

In alt.engineering.electrical Don Kelly wrote:
| ----------------------------
| "daestrom" wrote in message
| ...
|
| wrote in message
| ...
| In alt.engineering.electrical Michael Moroney
| wrote:
|
| | Are the load tap generators configured make-before-break?
| | Break-before-make would mean a (very short) power outage every
| activation
| | but make-before-break would mean a momentarily short-circuited winding
| and
| | the break would involve interrupting a large short circuit current.
|
| I wonder how much regulation could be managed through the use of variable
| leakage inductance in the transformer windings.
|
|
| I suppose you could, but increasing leakage inductance means you're
| increasing losses aren't you? Just a percent or two on a unit rated for
| 250 MVA can be too much to tolerate.
|
| daestrom
| -------------
| I don't see changing leakage inductance having much effect on losses ( a
| great effect on voltage regulation -likely all to the bad) but the problem
| is one of changing leakage inductance.
| Does this mean changing a gap in the core? Does it mean moving one winding
| with respect to another? In any case it does mean some fiddling with the
| core or winding.

The thought is to change the core in some way. Maybe that can be done in a
gradual way, as opposed to winding taps that have to be either BtM or MtB.


| This has been done for series lighting circuits where the load current was
| kept constant by using a transformer which balanced the forces between coils
| against a fixed weight. If the current changed the secondary coil moved so
| that there was more or less leakage. The units that I have seen were rather
| cumbersome.

I'm thinking more along the lines of a motor drive to move the coil, and
that be controlled by the same authority that would have controlled the
steppable taps.


Some years ago I worked at an Air Base in Northern Thailand. the
airfield lighting was a constant current series circuit and used
transformer as you describe - a movable core winding that was driven
in and out of the outer windings by a motor controlled by a current
sensing system.

I believe that street light systems are similar.

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

On May 13, 10:30 pm, wrote:

Is this the system where the voltage is 133 volts relative to ground and 230
volts between phases (and formerly 127 volts relative to ground and 220 volts
between phases)?

Since I'm posting from GoogleGroups I can't respond to Phil, but the
rest of you can be enlightened.

In 120/240 or similar systems there is not the freedom to choose this
ratio. The wiring of the source transformer determines it. As others
have noted, in the "Edison" U.S. system the source is a center tapped
transformer with the center tap grounded. This makes a two phase
system with each 120v "leg" 180 degrees out of phase with the other
one. The ratio of the high voltage (240v) and the low voltage (120v)
is always therefore 2:1.

In a three phase system there will be three transformers with
secondaries (one for each phase) wired in a "star" or "Y"
configuration. This is necessary because you need the center point of
the "star" or "Y" to be ground for each low voltage phase. If you wire
with a "delta" configuration there is no central grounding point
available for the individual phases. IN three phase circuits the
relationship between that individual phases to ground (say 120v) and
the voltage measured between phases is not arbitrary. It is always
determined by the square root of 3. Hence the between phase voltages
being sqrt 3 x 120 = 208V. Just like the two phase system these
ratios are determined by physics and can't be arbitrarily set.

Of course there is the issue that electric companies often will name a
voltage one thing while actually supplying an other for small
variations about the "standard" voltage.

Ï Ýãñáøå óôï ìÞíõìá
...
In alt.engineering.electrical Tzortzakakis Dimitrios
wrote:
|
| ? ?????? ??? ??????
| ...
| In alt.engineering.electrical Tzortzakakis Dimitrios

| wrote:
|
| | A shame that Tesla won the infamous "battle" and we don't have DC:-()
| But
| | then, we would be having a power plant at each neighborhood, instead
of
| the
| | 300 MW ones.
|
| And the latter make easy terrorism targets, too.
|
| I cross my fingers that terrorists get no electrical engineering
degree:0

I suspect quite many already have them. Many have degrees in a lot of
other
things like chemistry and physics. Some even have doctoral level degrees.


| | I know, I know, my answer was a bit provocative:-) And of course
there
| are
| | DC regulators.... You're talking about DC generators;the one a 300 MW
| uses
| | for excitation is 220 V, 1000 A DC and probably shunt field. I have
seen
| | here in some machine shops the old type welding generator, which is a
3
| | phase induction motor coupled to (usually) a compound field DC
| generator,
| | which provides the welding current. The modern ones are, maybe, not
| larger
| | than a shoe box and powered by a higher wattage 230 V 16 A
receptacle.
| | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers
and
| the
| | like).
|
| You don't use 400 V for anything heavy duty like an oven?
|
| Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and
| earth, goes without saying). Just if you connect it on 1 phase (as
usually)
| you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230
V is
| powerful enough for almost everything in a house, only large
airconditioners
| are 3 phase, and all industrial motors, even if they are 1HP:-) (

That means each element individually runs on 230 V and they just divided
them
up in three approximately equal sections, or use triple elements for each
type
of use.

How many things that have just ONE (large) element would have it available
in
both 230 V and 400 V versions?

Professional washing machines. One of my very first days 'in the field' was
to connect some of them. They have a large heating element, you can connect
it single phase, or 3 phase, it just heats up faster (of course) when you
connect it 3 phase. (they have a single phase motor, so it works also in
pure 230 V).


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

? "daestrom" ?????? ??? ??????
...

"Tzortzakakis Dimitrios" wrote in message
...

? "daestrom" ?????? ??? ??????
...

"Michael Moroney" wrote in message
...
"daestrom" writes:


P.S. In the US, a 'tap-changer' may be built for either for unloaded
or
loaded operation. The 'unloaded' type can not be stepped to another
tap
while there is load on the unit (although it can still be energized).
It's
switch contacts cannot interrupt load though, so if you try to move it
while
loaded, you can burn up the tap-changer. The classic
'load-tap-changer' is
actually several switches that are controlled in a precise sequence to
shift
the load from one tap of the transformer to another while not
interrupting
the load current.

P.P.S. Load tap changers typically have a significant time-delay built
into
the controls so they do not 'hunt' or respond to short drops in voltage
such
as starting a large load. 15 seconds to several minutes is typical.
So
even with load-tap-changers, starting a single load that is a high
percentage of the system capacity will *still* result in a voltage dip.

Are the load tap generators configured make-before-break?
Break-before-make would mean a (very short) power outage every
activation
but make-before-break would mean a momentarily short-circuited winding
and
the break would involve interrupting a large short circuit current.

Certainly modern ones likely use thyristors and zero crossing
detectors.


I figured someone would 'bite' :-)

Typical large power load-tap-changers have a primary winding and two
secondaries.
You mean a secondary and a tetriary? The transformer for the hotel load
of a 300 MW unit is powered directly from the turbo alternator (21 kV)
and has a secondary of 6.6 kV and a tetriary of again 6.6 kV. This is
done because it has wye-wye-wye connection (IIRC). The hotel load of such
a unit is 10%, also 30 MW, including 7 brown coal mills. Typical size of
a 6.6 kV motor is 1 MW.
One secondary produces about 100% of 'rated' secondary voltage. The
second secondary produces about 15% to 20% of the rated voltage, but has
numerous taps from end to end, about 2.5% 'steps'. (for a total of about
eight taps). The cental tap of the boost/buck winding is tied to one end
of the main secondary. The boost/buck can be used to step from 90% to
110% of the 'design' output. I suppose some can step over a wider range,
but I haven't run across them.

*TWO* rotary switches have each tap tied to one of the positions of each
rotory switch, and each 'wiper' is tied to single heavier contacts that
are opened in the operating sequence. The output side of these two
interrupting contacts are tied to each end of a large center-tapped
inductor.

So, normally both rotary switches are aligned to the same transformer
tap, both interrupting contacts are shut, and load current flows from
the boost/buck winding tap, splits and flows through both rotary
switches, both interrupting contacts, enters both ends of the inductor
and out the inductor center tap. Because the current flows into both
ends of the inductor and the mutual inductance of the two parts cancel,
there is little voltage drop in the inductor.

Begin step sequence:
1) Open one interrupting contactor. Now load current doubles through
half the inductor and is zero in the other half, so the voltage drop
across the inductor actually makes output voltage drop, even if trying
to step 'up'.
2) Move associated rotary switch to next step of transformer bank.
3) Close interrupting contactor. Now, the two rotary switches are
across different taps. The inductor prevents a excessive current,
otherwise you have a direct short of the two winding taps. Some tap
changers can stop at this point and are called 'half-step' units.
Obviously, the inductor has to be rated for sustained operation across a
step of the boost/buck winding plus load current in order to survive
sustained 'half step' operation.
4) But for tap changers that can't operate 'half-step', the sequence
continues. And opens the other interrupting contactor. Now the other
half of the inductor has full load current.
5) Move second rotary switch to next step (now both switches are on the
new step)
6) Close the second interrupting contactor. You're back in the initial
configuration, but with both rotary switches on a new transformer tap.
Quite the same principle is done with diesel locomotives and is called
diesel-electric transmission, and also in pure electric locomotives
(E-Lok in german, for Elektrische Lokomotive). The diesel engine,
2-stroke and usually 600 to 900 rpm at full throttle, is coupled to a
generator. The generator has small windings, connected in series for the
last notch, higher voltage and relatively smaller current, and in
parallel for start, higher amperage and smaller voltage. The traction
motors are directly coupled on the wheel shaft, and are air cooled. An
E-Lok has a trasformer, with the primary directly supplied by the
cetenary, 15 kV 16 2/3 Hz in Germany, and 25 kV 50 Hz in Greece, The
secondary uses the same principle. The typical size of a traction motor
is 1 MW, 4 (one each shaft) and maximum voltage 700 volts, and are series
wound motors with special construction to operate at 16 2/3 Hz (or 50 Hz
with today's technology). Typical power of a diesel locomotive is 2850
HP, while an electric is 6000 HP. with 1500 HP at each shaft, also ~1MW.
There is a heavy duty 12,000 HP diesel engine in USA(with 6 shafts, also
2000 HP at each shaft). The high speed ICE train (InterCityExpress) in
germany is 13,000 HP, has a normal travelling speed of 200 km/h, 2
locomotives, 3-phase induction motors, electronic drive.

In US, diesel-electric used to always be DC machines, but modern ones are
now AC generators with thyristers to regulate the power flow to the
traction motors. Traction motors are still DC however to allow for their
use in dynamic braking.

I suppose in Europe the better way to go would be regenerative braking,
putting the braking power back into the overhead line, but that would need
a static inverter. Probably the transformer secondary has a four-quadrant
converter to allow reversal of power flow ??

This is for sure in ICE, where they get 15 kV 16 2/3 Hz AC from the
cetenary, and they convert it to 3 -phase AC for traction motors (3 phase
induction), and they also use regenerative breaking.There's also the french
TGV (Tren de Grand Vitesse) and the just new by Alstom (www.alstom.com) AGV
(Autometrisse de Grand Vitesse). Classic E-Loks have regular breaking, and
AC motors with series excitation, designed to work at 16 2/3 Hz. (Just like
the ones you'll find in a drill, but much larger, at 1 MW or more). They are
called universal motors, in the small scale, because they can work both in
AC and DC. I'm wondering, how large their brushes are... In the 300 MW turbo
generator, the brushes that suplly the excitation current, are as large as
bricks. Newer type of turbo generators are brushless. The speed record for a
classic E-Lok is held by Siemens' Taurus, IIRC 180 km/h with 12,000 HP.
Nice thing about the newer solid-state control systems (AC-Generator/
DC-Traction) is the ability to control wheel-slip. In the old days it
took a skilled engineer (the train-driving kind) to get maximum power
without slipping a lot (and wasting a lot of sand). Now modern units have
speed sensors on each individual wheel set and control the power flow to
individual traction motors. As soon as a wheel set starts to slip it can
redirect power flow to other traction motors to prevent the slipping set
from 'polishing the rail'. This prolongs life of the wheels and rail and
actually improves the maximum tractive effort a locomotive can deliver.
And when hauling 100+ cars of coal in a unit train up grade, tractive
effort is what keeps you moving.

I have no idea about train driving, but in Germany I got a local train from
a small city to Mannheim, and the Lokfuehrer (train driver) was driving it
like a race car... He accelerated fully to 130 km/h, and when he was close
to the next stop, he braked fully, too. It had one E-Lok, and two cars.
Also, the ICE starts like a race car. It's longer than 500 m, 12 cars, and I
think it accelerates to 100 km/h in 10 seconds.
You forgot to mention that traction motors often have separately powered
blower motors for air-cooling. This is because the motor may spend hours
operating at low speeds and shaft-mounted cooling fans are not enough.
The motor blower is usually mounted up inside the engine house and
connects to the traction motor via a large flexible duct.

Yeah, right, and the transformer is cooled by active oil cooling (that means
that the oil cools the trasformer, and there's a separate oil cooler. Like
the intercooler used in the tanks where I served at army, but that's a
differrent story).
Some diesel-electric unitl have six axles and six traction motors. The
trade-off is between how much power you can get to the traction motors and
how much weight you can keep on the wheels to keep them from slipping.
Sand is okay for starting and some special situations, but you can't carry
enough to use it for an entire run. But of course too much weight and you
need more axles to protect the rail from damage (depending on the size of
the rail being used).

But isn't a locomotive by itself heavy enough? Like 120 tons and above, with
fuel and all?
(Check at www.wartsila.com some large diesels). In our new power station,
they have installed two 50 MW, 70,000 HP two-stroke diesels. To see how
2-stroke diesels work, look in www.howstuffworks.com.. The ships that travel
from Iraklion to Piraeus (the harbour of Athens) the new ones, have 4
Wartsila 12 V 46 4-stroke diesels. 12 is number of cylinders, in V, and with
a diameter of piston, 46 cm. When they travel normally at night, they fire
up 2 engines. But, when they make a day trip, they fire up all 4 engines at
full throttle, and the whole ship vibrates. A ship is the only place you can
get free electricity. In my last trip, I saw young students plugging their
laptops to the ship's receptacles. A free lunch, after all:-)
daestrom
P.S. As you can see, I've seen a few railroad locomotives as well.
Mostly just the older EMD's though, not GE's newer 'green' units.
I have no idea what they are doing in continental Greece, they *should* have
electrified all routes.



--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

writes:

In alt.engineering.electrical Thomas Tornblom wrote:

| Residential power in Norway is normally 230V three phase btw, instead
| of 400V three phase. Their 230V outlets are two phase and ground
| instead of one phase, neutral and ground. Their three phase outlets
| therefore are blue instead of red and have four prongs instead of five.

Is this the system where the voltage is 133 volts relative to ground and 230
volts between phases (and formerly 127 volts relative to ground and 220 volts
between phases)?

Yes.


If they still use that system, then I'm interested in buying a UPS designed
for that. But it is my understanding it is phased out in cities and hard to
find anymore in rural locations.

It seems they are moving to 400V as well, but I know many Norwegians
are paying a hefty premium on their three phase equipment, like
heatpumps.

My heatpump use an internally star configured 3x400V compressor, and
it would have been easy to wire it for 3x230V if they had brought out
all the leads.

In alt.engineering.electrical Tzortzakakis Dimitrios wrote:

| Professional washing machines. One of my very first days 'in the field' was
| to connect some of them. They have a large heating element, you can connect
| it single phase, or 3 phase, it just heats up faster (of course) when you
| connect it 3 phase. (they have a single phase motor, so it works also in
| pure 230 V).

If it has 3 elements rated for 230 volts, with 3 separate connections that
would be to three separate phase for a three phase feed, and all connected
to the one phase for a single phase feed, then it should heat up at the same
speed, while drawing three times the current (not accounting for the motor).

I don't know why it should heat up faster in three phase, or why you would
say "of course" about it. I would think it would heat up faster if you took
it over to London and hooked it up to a 240 volt supply.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Benj wrote:

| Since I'm posting from GoogleGroups I can't respond to Phil, but the
| rest of you can be enlightened.

Actually, I do see the ones the respond to my own posts. I think the reader
does that to keep the threading intact. New posts I won't see. And that is
what most of the spam is (I've seen some spammers that do followups to other
posts).


| In 120/240 or similar systems there is not the freedom to choose this
| ratio. The wiring of the source transformer determines it. As others
| have noted, in the "Edison" U.S. system the source is a center tapped
| transformer with the center tap grounded. This makes a two phase
| system with each 120v "leg" 180 degrees out of phase with the other
| one. The ratio of the high voltage (240v) and the low voltage (120v)
| is always therefore 2:1.
|
| In a three phase system there will be three transformers with
| secondaries (one for each phase) wired in a "star" or "Y"
| configuration. This is necessary because you need the center point of
| the "star" or "Y" to be ground for each low voltage phase. If you wire
| with a "delta" configuration there is no central grounding point
| available for the individual phases. IN three phase circuits the
| relationship between that individual phases to ground (say 120v) and
| the voltage measured between phases is not arbitrary. It is always
| determined by the square root of 3. Hence the between phase voltages
| being sqrt 3 x 120 = 208V. Just like the two phase system these
| ratios are determined by physics and can't be arbitrarily set.

There is no more or less option to choose once you have either system. The
choice you have is between the systems. If you have single phase, you only
get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a
ratio.


| Of course there is the issue that electric companies often will name a
| voltage one thing while actually supplying an other for small
| variations about the "standard" voltage.

They call it 208 volts, but it's closer to 207.8460969 :-)

Precise voltage is not really practical. The voltage standard is a target to
stay near.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Thomas Tornblom wrote:
| writes:
|
| In alt.engineering.electrical Thomas Tornblom wrote:
|
| | Residential power in Norway is normally 230V three phase btw, instead
| | of 400V three phase. Their 230V outlets are two phase and ground
| | instead of one phase, neutral and ground. Their three phase outlets
| | therefore are blue instead of red and have four prongs instead of five.
|
| Is this the system where the voltage is 133 volts relative to ground and 230
| volts between phases (and formerly 127 volts relative to ground and 220 volts
| between phases)?
|
| Yes.
|
|
| If they still use that system, then I'm interested in buying a UPS designed
| for that. But it is my understanding it is phased out in cities and hard to
| find anymore in rural locations.
|
| It seems they are moving to 400V as well, but I know many Norwegians
| are paying a hefty premium on their three phase equipment, like
| heatpumps.
|
| My heatpump use an internally star configured 3x400V compressor, and
| it would have been easy to wire it for 3x230V if they had brought out
| all the leads.

If all 6 leads of the 3 windings are brought out separate, then it can be wired
in star for 400/230 volt systems, and in delta for 230/133 volt systems. But
for Europe in general there would be little reason to do that. There is also
no reason to do that in North America, as we don't have any 360/208 volt systems
at all.

If I were in Europe I'd rather than the 400/230 volt system. In North America
I'd rather have the 480/277 volt system.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

"daestrom" writes:


wrote in message
...

What about multiple parallel transformers, or at least multiple parallel
windings on the same core (on whichever side the tapping is to be done),
where the taps are stepped incrementally on each winding? Instead of a
shorted winding segment, you'd have windings of differing voltage in
parallel as each of the windings change their taps one at a time.

That's still essentially a shorted turn (or set of turns).

So when one is set for say 118V and the other is set for 120V, you have a
118V source connected in parallel with a 120V source and the only impedance
is the transformer windings??

OUCH!!! I think the magic smoke will be spewing in no time

Phil, did you see daestrom's excellent explanation how they use an
inductor to prevent a dead short but in a way such that the inductor is
virtually not there during normal operation (counterflowing currents)?

If these tap changers are rather expensive, I'm wondering what those
pole pig "voltage regulators" I mentioned are. I thought they were just
tapped autotransformers.

writes:

In alt.engineering.electrical Thomas Tornblom wrote:
| writes:
|
| In alt.engineering.electrical Thomas Tornblom wrote:
|
| | Residential power in Norway is normally 230V three phase btw, instead
| | of 400V three phase. Their 230V outlets are two phase and ground
| | instead of one phase, neutral and ground. Their three phase outlets
| | therefore are blue instead of red and have four prongs instead of five.
|
| Is this the system where the voltage is 133 volts relative to ground and 230
| volts between phases (and formerly 127 volts relative to ground and 220 volts
| between phases)?
|
| Yes.
|
|
| If they still use that system, then I'm interested in buying a UPS designed
| for that. But it is my understanding it is phased out in cities and hard to
| find anymore in rural locations.
|
| It seems they are moving to 400V as well, but I know many Norwegians
| are paying a hefty premium on their three phase equipment, like
| heatpumps.
|
| My heatpump use an internally star configured 3x400V compressor, and
| it would have been easy to wire it for 3x230V if they had brought out
| all the leads.

If all 6 leads of the 3 windings are brought out separate, then it can be wired
in star for 400/230 volt systems, and in delta for 230/133 volt systems. But
for Europe in general there would be little reason to do that. There is also
no reason to do that in North America, as we don't have any 360/208 volt systems
at all.

It would allow the Norwegians to buy less expensive heatpumps from Sweden :-)

It seems like a very simple and cheap thing to do.

----------------------------
wrote in message
...
In alt.engineering.electrical Don Kelly wrote:

| Yes -you are shorting a part of the winding but the switching is a bit
more
| complex than that so that short circuit currents are limited to
reasonable
| values. It is a multistep operation with reactor switching. On-load tap
| changers are expensive and are generally limited to applications where
this
| is absolutely needed (I have seen one where the tap changer was nearly
as
| large as the transformer).

I was thinking of what I might do to get some fine voltage control within
a
very limited range around 120 volts. The obvious option was a 0-140 volt
variable transformer. But I wanted to make sure I had a setup that could
be better limited, for example, to not allow an accidental too low
voltage.
I also didn't want to run all the power through the variable. So what I
was going to do was get a smaller variable transformer, and two buck-boost
transformers. One transformer would be wired 120-16 in buck mode to drop
the voltage down to 104. The other transformer would be wired 120-24 and
supplied via the 0-140 variable transformer, giving me a 0-28 variable
boost.
The end result is 104-132 over the full range of variable transformer
control
(assuming the boost transformer has no issues with being overfed at 140V).

So I might envision a transformer where the taps can be part of a boost
transformer added to the main transformer. The first buck transformer in
my above example would not be needed because the main transformer would be
designed with a 1st secondary at the lowest voltage of the adjustable
range.
A 2nd secondary on the same main transformer would have the adjustable
taps
and it would feed a separate boost transformer which has a secondary wired
in series with the 1st secondary of the main. So the taps would only be
dealing directly with a fraction of the power (assuming there is no back
feed issue involved) based on the needed adjustment range.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to
ignorance |
| by the abuse department, bellsouth.net is blocked. If you post
to |
| Usenet from these places, find another Usenet provider ASAP.
|
| Phil Howard KA9WGN (email for humans: first name in lower case at
ipal.net) |

--------------
If I read you correctly, you want to use a second secondary (lower power
rating) which is tapped and put in series with the main secondary. Now once
you do this, you have in effect a single secondary with taps just as in a
conventional tapped secondary. Sure the "tapped section" is lower power-
because it is a lower voltage but it still has to handle the same current.
Nothing is gained.
The problem in tap changing is not "power" but the current being switched.

In either case the voltage driving short circuit current on tap changing is
that between taps
Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in
turns between taps. The short circuit current on such a change will be
proportional to 1/(delta n).

If you want fine control, then you could go to sliding carbon brush as in a
variac. The first idea of a separate transformer feeding a variac will not
solve the "too low" voltage problem of the variac because you are still
dealing with an autotransformer.


Don Kelly
remove the X to answer

----------------------------
wrote in message
...
In alt.engineering.electrical Benj wrote:

| Since I'm posting from GoogleGroups I can't respond to Phil, but the
| rest of you can be enlightened.

Actually, I do see the ones the respond to my own posts. I think the
reader
does that to keep the threading intact. New posts I won't see. And that
is
what most of the spam is (I've seen some spammers that do followups to
other
posts).


| In 120/240 or similar systems there is not the freedom to choose this
| ratio. The wiring of the source transformer determines it. As others
| have noted, in the "Edison" U.S. system the source is a center tapped
| transformer with the center tap grounded. This makes a two phase
| system with each 120v "leg" 180 degrees out of phase with the other
| one. The ratio of the high voltage (240v) and the low voltage (120v)
| is always therefore 2:1.
|
| In a three phase system there will be three transformers with
| secondaries (one for each phase) wired in a "star" or "Y"
| configuration. This is necessary because you need the center point of
| the "star" or "Y" to be ground for each low voltage phase. If you wire
| with a "delta" configuration there is no central grounding point
| available for the individual phases. IN three phase circuits the
| relationship between that individual phases to ground (say 120v) and
| the voltage measured between phases is not arbitrary. It is always
| determined by the square root of 3. Hence the between phase voltages
| being sqrt 3 x 120 = 208V. Just like the two phase system these
| ratios are determined by physics and can't be arbitrarily set.

There is no more or less option to choose once you have either system.
The
choice you have is between the systems. If you have single phase, you
only
get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a
ratio.


| Of course there is the issue that electric companies often will name a
| voltage one thing while actually supplying an other for small
| variations about the "standard" voltage.

They call it 208 volts, but it's closer to 207.8460969 :-)

Precise voltage is not really practical. The voltage standard is a target
to
stay near.
-------------

Just a bitch that we have dealt with befo

Phil- please realize that 207.846096....... is meaningless except that it is
"about 208". 208V is correct to 3 significant figures which is actually
better than one can assume to be true in practice. If the voltage line to
neutral is actually 120.V (note the decimal) then we have 3 significant
digits implying something between 119.5 Vand 120.5.V
Then all you can truly claim is 208.V
If it is 120.0V then there is reason to assume 208.0 V but no more decimals
than that.
If you have a meter which gives you 120.000000V with less than 1 part in 120
million error then you can claim 207.846097V for line to line voltage Do
you have such a meter?

Engineering and physics students who ignore the principle of "significant
digits" lose marks for this "decimal inflation".

Sure- you can let the calculator carry the extra digits (as it will do
internally) but accepting these as gospel truth to the limit of the
calculator or computer display is simply not on as you can't get better
accuracy from a calculation than the accuracy of the original data (actually
you will lose a bit). All that you get rid of is round off errors in
calculations.

Since, as you say, precise voltage is not really practical, then
multi-decimal point numbers are meaningless. If we say 120V +/-10% then we
are talking about 108-132V which for line to line becomes 187-229V (average
208V) and any extra decimal points don't mean anything.

Don Kelly
remove the X to answer

----------------------------
wrote in message
...
In alt.engineering.electrical Don Kelly wrote:

| Yes -you are shorting a part of the winding but the switching is a bit
more
| complex than that so that short circuit currents are limited to
reasonable
| values. It is a multistep operation with reactor switching. On-load tap
| changers are expensive and are generally limited to applications where
this
| is absolutely needed (I have seen one where the tap changer was nearly
as
| large as the transformer).

What about multiple parallel transformers, or at least multiple parallel
windings on the same core (on whichever side the tapping is to be done),
where the taps are stepped incrementally on each winding? Instead of a
shorted winding segment, you'd have windings of differing voltage in
parallel as each of the windings change their taps one at a time.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to
ignorance |
| by the abuse department, bellsouth.net is blocked. If you post
to |
| Usenet from these places, find another Usenet provider ASAP.
|
| Phil Howard KA9WGN (email for humans: first name in lower case at
ipal.net) |
------------
So you have a differential voltage producing a circulating current through
both windings leading to losses and heating due to circulating currents. In
addition, there would be shifts in the load sharing between the two
secondaries- with the possibility of overloading one of them. Also, you
still haven't solved the problem of switching the current from one tap to
another Note also to shift 2% you would have to make two 2% shifts, one on
each winding so that you are essentially doubling the work and tap changing
equipment while introducing other problems as Daestrom has indicated.
-

--

Don Kelly
remove the X to answer

In alt.engineering.electrical Don Kelly wrote:

| If I read you correctly, you want to use a second secondary (lower power
| rating) which is tapped and put in series with the main secondary. Now once
| you do this, you have in effect a single secondary with taps just as in a
| conventional tapped secondary. Sure the "tapped section" is lower power-
| because it is a lower voltage but it still has to handle the same current.
| Nothing is gained.
| The problem in tap changing is not "power" but the current being switched.

No, that is not what I tried to explain. I'll try again:

The main transformer would have 2 secondaries. These 2 secondaries are NOT
wired in series with each other. The smaller of these secondaries will have
taps. The tapped smaller secondary feeds another smaller transformer. The
larger secondary of the main transformer, and the only secondary of the smaller
auxiliary transformer, would be wired in series. So the taps are only dealing
with the current of the lower power "tapping section". The smaller secondary
of the main transformer, and the primary of the auxiliary transformer, can be
wired for whatever voltage/current works out best.


| In either case the voltage driving short circuit current on tap changing is
| that between taps
| Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in
| turns between taps. The short circuit current on such a change will be
| proportional to 1/(delta n).
|
| If you want fine control, then you could go to sliding carbon brush as in a
| variac. The first idea of a separate transformer feeding a variac will not
| solve the "too low" voltage problem of the variac because you are still
| dealing with an autotransformer.

In that first scheme, adjusting the variac to the lowest voltage would be
reducing the voltage contributed by the boost transformer. There is still
the original supply voltage going around the variac, "plus" (actually minus)
the buck voltage (to select the range I want). Since the variac is an
autotransformer itself, it merely feeds the primary of the boost transformer.
Note that in this case the "boost" transformer is wired as an isolation
transformer. I should have mentioned that. If needed, I guess I could draw
some ASCII diagrams or try to get something made graphically (all the tools
I have to do that suck, except for Visio which needs Windows to run and I
don't have a spare machine to do that at the moment).

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical daestrom wrote:
|
| wrote in message
| ...
| In alt.engineering.electrical Don Kelly wrote:
|
| | Yes -you are shorting a part of the winding but the switching is a bit
| more
| | complex than that so that short circuit currents are limited to
| reasonable
| | values. It is a multistep operation with reactor switching. On-load tap
| | changers are expensive and are generally limited to applications where
| this
| | is absolutely needed (I have seen one where the tap changer was nearly
| as
| | large as the transformer).
|
| What about multiple parallel transformers, or at least multiple parallel
| windings on the same core (on whichever side the tapping is to be done),
| where the taps are stepped incrementally on each winding? Instead of a
| shorted winding segment, you'd have windings of differing voltage in
| parallel as each of the windings change their taps one at a time.
|
|
| So when one is set for say 118V and the other is set for 120V, you have a
| 118V source connected in parallel with a 120V source and the only impedance
| is the transformer windings??
|
| OUCH!!! I think the magic smoke will be spewing in no time

I was afraid of that.

That also means if you are going to parallel 2 transformers, they better have
exactly the same winding ratio.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Michael Moroney wrote:

| Phil, did you see daestrom's excellent explanation how they use an
| inductor to prevent a dead short but in a way such that the inductor is
| virtually not there during normal operation (counterflowing currents)?

I believe I missed that.


| If these tap changers are rather expensive, I'm wondering what those
| pole pig "voltage regulators" I mentioned are. I thought they were just
| tapped autotransformers.

Sounds like they may be more of a voltage selector.

One set of transformers I saw once had a voltage selector which also revealed
the voltage to me. Even those these huge things were well guarded behind a
chainlink fence with barbed wire on top, I could clearly read the instructions
on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
range (I believe that was a middle one). The secondaries were a thick bundle
of insulated wires not on insulator standoffs, so obviously LV, possibly 480V
or 208V. These were 3 single tank transformers in roughly the design style
of a pole pig (round tank) with a control panel on them with the tap control
and some gauge I guessed may be temperature (but I could not see it clear
enough at the distance I was at to be sure). The instructions did indicate
that the transformer must be de-energized (not just unloaded) when making the
change. So I'm guessing they were just to compensate for variations in the
delivered voltage. These transformers were about 1 meter wide and 2.5 meters
high, each (3 of them). I did not see any reference to a kVA rating. They
were also very old looking (pre-WWII). They were humming.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Don Kelly wrote:

| Just a bitch that we have dealt with befo
|
| Phil- please realize that 207.846096....... is meaningless except that it is
| "about 208". 208V is correct to 3 significant figures which is actually
| better than one can assume to be true in practice. If the voltage line to
| neutral is actually 120.V (note the decimal) then we have 3 significant
| digits implying something between 119.5 Vand 120.5.V
| Then all you can truly claim is 208.V
| If it is 120.0V then there is reason to assume 208.0 V but no more decimals
| than that.
| If you have a meter which gives you 120.000000V with less than 1 part in 120
| million error then you can claim 207.846097V for line to line voltage Do
| you have such a meter?
|
| Engineering and physics students who ignore the principle of "significant
| digits" lose marks for this "decimal inflation".
|
| Sure- you can let the calculator carry the extra digits (as it will do
| internally) but accepting these as gospel truth to the limit of the
| calculator or computer display is simply not on as you can't get better
| accuracy from a calculation than the accuracy of the original data (actually
| you will lose a bit). All that you get rid of is round off errors in
| calculations.
|
| Since, as you say, precise voltage is not really practical, then
| multi-decimal point numbers are meaningless. If we say 120V +/-10% then we
| are talking about 108-132V which for line to line becomes 187-229V (average
| 208V) and any extra decimal points don't mean anything.

You didn't notice the :-) I put on the number?

We've been over this. I know the practice of significant digits, and how
the voltages are designated (two different reasons you can get 208). I do
follow the practice of carrying exactly the result of calculations into
other calculations. I also use over significance in comparison of numbers.

But I also know that rounding is a form of noise. So I avoid it until the
time I end up with the final result. So if I multiply 120 by the square
root of three I do get a number like 207.84609690826527522329356 which is
either carried as-is into the next calculation, or rounded if it is the
final answer. If some other strange calculation happens to give me the
value 207.84609690826527522329356 then I know it is effectively equivalent
to 120 times the square root of three in some way. But if what I get is
208.455732193971783228 then I know it has nothing to do with 120 times the
square root of three, even though it, too, would end up as 208 if rounded
to 3 significant digits.

When it comes to _measured_ amounts, as opposed to synthetic ones, then the
significance rules dictate how to round the results. With synthetic numbers
(e.g. numbers I can just pick), I can also pick the rounding rules for the
final results. But if I don't know that the calculations are done (e.g. I
am not merely giving a designation for a voltage system), where someone else
may take those numbers and do more calculations and round the results, then
I do use more significance. But that is no different to me than just carrying
that number from one calculation stage to another.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

In alt.engineering.electrical Thomas Tornblom wrote:
| writes:
|
| In alt.engineering.electrical Thomas Tornblom wrote:
| | writes:
| |
| | In alt.engineering.electrical Thomas Tornblom wrote:
| |
| | | Residential power in Norway is normally 230V three phase btw, instead
| | | of 400V three phase. Their 230V outlets are two phase and ground
| | | instead of one phase, neutral and ground. Their three phase outlets
| | | therefore are blue instead of red and have four prongs instead of five.
| |
| | Is this the system where the voltage is 133 volts relative to ground and 230
| | volts between phases (and formerly 127 volts relative to ground and 220 volts
| | between phases)?
| |
| | Yes.
| |
| |
| | If they still use that system, then I'm interested in buying a UPS designed
| | for that. But it is my understanding it is phased out in cities and hard to
| | find anymore in rural locations.
| |
| | It seems they are moving to 400V as well, but I know many Norwegians
| | are paying a hefty premium on their three phase equipment, like
| | heatpumps.
| |
| | My heatpump use an internally star configured 3x400V compressor, and
| | it would have been easy to wire it for 3x230V if they had brought out
| | all the leads.
|
| If all 6 leads of the 3 windings are brought out separate, then it can be wired
| in star for 400/230 volt systems, and in delta for 230/133 volt systems. But
| for Europe in general there would be little reason to do that. There is also
| no reason to do that in North America, as we don't have any 360/208 volt systems
| at all.
|
| It would allow the Norwegians to buy less expensive heatpumps from Sweden :-)
|
| It seems like a very simple and cheap thing to do.

My guess is that in the cities, they have already changed over to a 400/230
system, or at least a 380/220 system that hasn't been voltage adjusted, yet.
What I've heard is the 220/127 system was a leftover in some rural areas of
Norway, and also in Spain. Apparently Suadi Arabia has this system so they
can make use of both European and American single phase appliances. Mexico
also has 220/127 but primarily uses the 127 volt connection (and it's 60 Hz).
The really strange thing is Brazil has 220 volts all around the country,
with 60 Hz in some parts and 50 Hz in others, and used to use the American
120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise
with that).

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

On 15 May 2008 05:20:27 GMT, wrote:

In alt.engineering.electrical Michael Moroney wrote:

| Phil, did you see daestrom's excellent explanation how they use an
| inductor to prevent a dead short but in a way such that the inductor is
| virtually not there during normal operation (counterflowing currents)?

I believe I missed that.


| If these tap changers are rather expensive, I'm wondering what those
| pole pig "voltage regulators" I mentioned are. I thought they were just
| tapped autotransformers.

Sounds like they may be more of a voltage selector.

One set of transformers I saw once had a voltage selector which also revealed
the voltage to me. Even those these huge things were well guarded behind a
chainlink fence with barbed wire on top, I could clearly read the instructions
on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
range (I believe that was a middle one). The secondaries were a thick bundle
of insulated wires not on insulator standoffs, so obviously LV, possibly 480V
or 208V. These were 3 single tank transformers in roughly the design style
of a pole pig (round tank) with a control panel on them with the tap control
and some gauge I guessed may be temperature (but I could not see it clear
enough at the distance I was at to be sure). The instructions did indicate
that the transformer must be de-energized (not just unloaded) when making the
change. So I'm guessing they were just to compensate for variations in the
delivered voltage. These transformers were about 1 meter wide and 2.5 meters
high, each (3 of them). I did not see any reference to a kVA rating. They
were also very old looking (pre-WWII). They were humming.


All distribution transformers, sometimes called "pole pigs", that I
have seen had some sort of voltage adjusting system, usually referred
to as taps. Usually they are an actual bolted "tap" and you open the
transformer and set the output voltage by making the proper tap
connection when the transformer is installed and frankly it is usually
ignored thereafter.

The other "cans" you often see on poles are capacitors used to adjust
the power factor on some secondaries.

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

daestrom wrote:

But the trouble with overall weight is the combination of weight, power
and rail capacity. When you get to larger units, the rail used on a lot
of roads can't handle more than about 50,000 lbm per wheel set. That
means you're limited to about 100 tons for a unit with just 2 axles per
truck (4 total). Go up to a 120 ton and you need 3 axles per truck.
But a 100 ton, 4-axle unit has 12,500 lbm per axle, while a 120 ton,
6-axle unit has only 10,000 lbm per axle. If the wheel friction
coefficients are the same, the 4-axle unit can develop 25% more tractive
effort when starting before slipping wheels.

lbm?

I'm not sure on your units.

In another life I used to calibrate railroad electronic weigh bridges.

4 axle locomotives were about 265,000 pounds (US).

6 axle locomotives were about 360,000 pounds.

One 3 axle drive truck weighed 65,000 pounds.
(In a second other life, hauled it on a flatbed truck.)

? "daestrom" ?????? ??? ??????
...

"Tzortzakakis Dimitrios" wrote in message
...

? "daestrom" ?????? ??? ??????
...

snip
Nice thing about the newer solid-state control systems (AC-Generator/
DC-Traction) is the ability to control wheel-slip. In the old days it
took a skilled engineer (the train-driving kind) to get maximum power
without slipping a lot (and wasting a lot of sand). Now modern units
have speed sensors on each individual wheel set and control the power
flow to individual traction motors. As soon as a wheel set starts to
slip it can redirect power flow to other traction motors to prevent the
slipping set from 'polishing the rail'. This prolongs life of the
wheels and rail and actually improves the maximum tractive effort a
locomotive can deliver. And when hauling 100+ cars of coal in a unit
train up grade, tractive effort is what keeps you moving.

I have no idea about train driving, but in Germany I got a local train
from a small city to Mannheim, and the Lokfuehrer (train driver) was
driving it like a race car... He accelerated fully to 130 km/h, and when
he was close to the next stop, he braked fully, too. It had one E-Lok,
and two cars. Also, the ICE starts like a race car. It's longer than 500
m, 12 cars, and I think it accelerates to 100 km/h in 10 seconds.

There is little doubt that electric trains are faster than other types as
far as acceleration and overall speed. :-)
Yes, because as the germans say-"Sie nehmen Strom direct aus der
Leitung"-They draw power directly from the wire. So it's a higher impulse
current than any on board diesel can provide;_)

snip
Some diesel-electric unitl have six axles and six traction motors. The
trade-off is between how much power you can get to the traction motors
and how much weight you can keep on the wheels to keep them from
slipping. Sand is okay for starting and some special situations, but you
can't carry enough to use it for an entire run. But of course too much
weight and you need more axles to protect the rail from damage
(depending on the size of the rail being used).

But isn't a locomotive by itself heavy enough? Like 120 tons and above,
with fuel and all?
(Check at www.wartsila.com some large diesels). In our new power station,
they have installed two 50 MW, 70,000 HP two-stroke diesels. To see how
2-stroke diesels work, look in www.howstuffworks.com..

I'm quite aware of how a 2-stroke works, as the large EMD's (654 series,
up to V-20 cylinder) that have been around for years are exactly that.
Also how the turbo-charger works, the four different lube-oil pumps
(scavenging, piston-cooling, main, and soak-back). Not to mention the
fuel injectors, overspeed trip, high-crankcase pressure shutdown, and
air-start systems to name a few of the various components. And
Westinghouse air brakes with several variations, and the MU (multi-unit)
interface used to connect several locomotives together and allow them all
to be 'driven' from one cab.
'
Of course you are, but I thought there might be other members of the group,
that don't. I didn't know until I read the article. The large, 15,000 HP, 11
MW diesels we have here at our local power station, have a final steam
stage, for better efficiency. The URL of our local college, where I got my
degree, is www.teiher.gr , but I'm not sure if they got an english version.

But the trouble with overall weight is the combination of weight, power
and rail capacity. When you get to larger units, the rail used on a lot
of roads can't handle more than about 50,000 lbm per wheel set. That
means you're limited to about 100 tons for a unit with just 2 axles per
truck (4 total). Go up to a 120 ton and you need 3 axles per truck. But
a 100 ton, 4-axle unit has 12,500 lbm per axle, while a 120 ton, 6-axle
unit has only 10,000 lbm per axle. If the wheel friction coefficients are
the same, the 4-axle unit can develop 25% more tractive effort when
starting before slipping wheels.

Of course if the 120 ton, 6-axle unit has more overall horsepower, then
even though it develops less tractive effort at low speeds, it can achieve
a higher speed when loaded to it's rated tractive effort. Below a certain
speed, the maximum you can pull is dictated by wheel slip. Then you're
limited by tractive motor cooling up to a second point. Beyond that, the
overall horsepower becomes the limit. Once you're 'horsepower limited',
you can go faster, but only if you can reduce the amount of tractive
effort needed (i.e. you want to go faster, you have to pull fewer cars or
not climb as steep a grade). This 'hp limited speed' is in the range of
just 15 to 20 mph for a lot of 4-axle units, somewhat faster for 6-axle
units.

With typical freight trains in the US, they look at the steepest grade on
the road and figure out enough locomotive units and maximum cars to just
be horsepower limited on that grade. So while the train may go faster on
less steep sections or level grade, it'll be at notch 8 (full throttle)
and struggling to make about 15 mph up the steepest part of the route.
And stalled if one of the locomotive units dies.

So more hp means you may be able to pull it faster, but you can't always
pull as much.

Kind of 'weird' until you work out a few problems, but that's how it
works.

In Germany, they have special locomotives for freight trains, and special
for passenger ones. The former desingned for larger traction power, the
latter for higher speed. I have more experience with ships, since there are
no railroads in Crete, but there's a lot of sea, and islands in Greece:-)
I'll never forget my trip to Rhodes, where my batallion was situated, by
rail from Korinthos (the infamous boot camp) and with ship to Rhodes. She
was full of soldiers and commuters:-)
NB.:There are railroads in continental Greece.


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

? "Bruce in Bangkok" ?????? ??? ??????
...
On 15 May 2008 05:20:27 GMT, wrote:

In alt.engineering.electrical Michael Moroney
wrote:

| Phil, did you see daestrom's excellent explanation how they use an
| inductor to prevent a dead short but in a way such that the inductor is
| virtually not there during normal operation (counterflowing currents)?

I believe I missed that.


| If these tap changers are rather expensive, I'm wondering what those
| pole pig "voltage regulators" I mentioned are. I thought they were just
| tapped autotransformers.

Sounds like they may be more of a voltage selector.

One set of transformers I saw once had a voltage selector which also
revealed
the voltage to me. Even those these huge things were well guarded behind
a
chainlink fence with barbed wire on top, I could clearly read the
instructions
on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
range (I believe that was a middle one). The secondaries were a thick
bundle
of insulated wires not on insulator standoffs, so obviously LV, possibly
480V
or 208V. These were 3 single tank transformers in roughly the design
style
of a pole pig (round tank) with a control panel on them with the tap
control
and some gauge I guessed may be temperature (but I could not see it clear
enough at the distance I was at to be sure). The instructions did
indicate
that the transformer must be de-energized (not just unloaded) when making
the
change. So I'm guessing they were just to compensate for variations in
the
delivered voltage. These transformers were about 1 meter wide and 2.5
meters
high, each (3 of them). I did not see any reference to a kVA rating.
They
were also very old looking (pre-WWII). They were humming.


All distribution transformers, sometimes called "pole pigs", that I
have seen had some sort of voltage adjusting system, usually referred
to as taps. Usually they are an actual bolted "tap" and you open the
transformer and set the output voltage by making the proper tap
connection when the transformer is installed and frankly it is usually
ignored thereafter.

The other "cans" you often see on poles are capacitors used to adjust
the power factor on some secondaries.

Or disconnect switches, plain or with high-voltage fuses.
Bruce-in-Bangkok

--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

Ï Ýãñáøå óôï ìÞíõìá
...
In alt.engineering.electrical Tzortzakakis Dimitrios
wrote:

| Professional washing machines. One of my very first days 'in the field'
was
| to connect some of them. They have a large heating element, you can
connect
| it single phase, or 3 phase, it just heats up faster (of course) when
you
| connect it 3 phase. (they have a single phase motor, so it works also in
| pure 230 V).

If it has 3 elements rated for 230 volts, with 3 separate connections that
would be to three separate phase for a three phase feed, and all connected
to the one phase for a single phase feed, then it should heat up at the
same
speed, while drawing three times the current (not accounting for the
motor).

I don't know why it should heat up faster in three phase, or why you would
say "of course" about it. I would think it would heat up faster if you
took
it over to London and hooked it up to a 240 volt supply.

Maybe you connected with single phase just one element? The rest two
remained unconnected? (3 230 volts elements, connected wye). I'm sure it
heated up faster, in 3 phase connection.





--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.

writes:

In alt.engineering.electrical Michael Moroney wrote:

| If these tap changers are rather expensive, I'm wondering what those
| pole pig "voltage regulators" I mentioned are. I thought they were just
| tapped autotransformers.

Sounds like they may be more of a voltage selector.

Probably.

One set of transformers I saw once had a voltage selector which also revealed
the voltage to me. Even those these huge things were well guarded behind a
chainlink fence with barbed wire on top, I could clearly read the instructions
on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
range (I believe that was a middle one). The secondaries were a thick bundle
of insulated wires not on insulator standoffs, so obviously LV, possibly 480V
or 208V. These were 3 single tank transformers in roughly the design style
of a pole pig (round tank) with a control panel on them with the tap control
and some gauge I guessed may be temperature (but I could not see it clear
enough at the distance I was at to be sure). The instructions did indicate
that the transformer must be de-energized (not just unloaded) when making the
change. So I'm guessing they were just to compensate for variations in the
delivered voltage. These transformers were about 1 meter wide and 2.5 meters
high, each (3 of them). I did not see any reference to a kVA rating. They
were also very old looking (pre-WWII). They were humming.

Interesting. Around here I see control boxes on the pole-mounted ones.
Maybe they have something to read. (I know some read SIEMENS in large
letters on some of them, apparently the manufacturer)

Long ago, during one of the past "oil crises" (1973 or 1978 or so) they
proposed cutting back the voltage delievered to one's home by 5-10% from
the normal voltage, a "brownout", "to save energy". I once wondered how
they may have done that, assuming any automated regulating equipment was
hardwired to provide 13.8kV or whatever, and that setting couldn't easily
be changed. Also, any automated regulators downstream would try to
compensate for the lower supply and raise their output voltage, so all
regulators would have to be adjusted. But if was done manually, for
equipment not tied to a particular voltage, they could do it on a
substation-by-substation basis, and ones "downstream" could have been
left alone.

Ï Ýãñáøå óôï ìÞíõìá
...
In alt.engineering.electrical Thomas Tornblom wrote:
| writes:
|
| In alt.engineering.electrical Thomas Tornblom wrote:
| | writes:
| |
| | In alt.engineering.electrical Thomas Tornblom wrote:
| |
| | | Residential power in Norway is normally 230V three phase btw,
instead
| | | of 400V three phase. Their 230V outlets are two phase and ground
| | | instead of one phase, neutral and ground. Their three phase
outlets
| | | therefore are blue instead of red and have four prongs instead of
five.
| |
| | Is this the system where the voltage is 133 volts relative to ground
and 230
| | volts between phases (and formerly 127 volts relative to ground and
220 volts
| | between phases)?
| |
| | Yes.
| |
| |
| | If they still use that system, then I'm interested in buying a UPS
designed
| | for that. But it is my understanding it is phased out in cities and
hard to
| | find anymore in rural locations.
| |
| | It seems they are moving to 400V as well, but I know many Norwegians
| | are paying a hefty premium on their three phase equipment, like
| | heatpumps.
| |
| | My heatpump use an internally star configured 3x400V compressor, and
| | it would have been easy to wire it for 3x230V if they had brought out
| | all the leads.
|
| If all 6 leads of the 3 windings are brought out separate, then it can
be wired
| in star for 400/230 volt systems, and in delta for 230/133 volt
systems. But
| for Europe in general there would be little reason to do that. There
is also
| no reason to do that in North America, as we don't have any 360/208
volt systems
| at all.
|
| It would allow the Norwegians to buy less expensive heatpumps from
Sweden :-)
|
| It seems like a very simple and cheap thing to do.

My guess is that in the cities, they have already changed over to a
400/230
system, or at least a 380/220 system that hasn't been voltage adjusted,
yet.
What I've heard is the 220/127 system was a leftover in some rural areas
of
Norway, and also in Spain. Apparently Suadi Arabia has this system so
they
can make use of both European and American single phase appliances.
Mexico
also has 220/127 but primarily uses the 127 volt connection (and it's 60
Hz).
The really strange thing is Brazil has 220 volts all around the country,
with 60 Hz in some parts and 50 Hz in others, and used to use the American
120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise
with that).

--
There should be no problem with the frequency, the local US base (In
Gournes-decomissioned after the end of the Cold War) used a regular 15 kV,
50 Hz feed, from the cretan grid, which was stepped down to 4150 volts and
then to 120/240. All with US switchgear and tranformers! (NB for US guys.#10
wire gauge-10 mm2 main feed of residence, #12 -6 mm2 stove,#14-4 mm2
water heaters, #16-2.5 mm2 washing machines, dryers, #18-1.5 mm2
lighting.-approximately). I think that the personnel of the base used
standard US fluorescent light fixtures and other equipment, sone of it was
left as some of the buildings "inherited" by the greek state, were converted
by us to 230/400 volts, with regular Schuko receptacles.


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.